Process and systems for purification of boron trichloride

ABSTRACT

Processes are disclosed for increasing the condensed phase production of BCl 3  comprising less than about 10 ppm phosgene, less than 10 ppm chlorine, and less than 10 ppm HCl. In one embodiment the process comprises injecting an inert gas into a container having condensed BCl 3  therein, the condensed BCl 3  having therein a minor portion of phosgene impurity. A major portion of the phosgene in the condensed BCl 3  is decomposed to carbon monoxide and chlorine by increasing temperature to produce a phosgene deficient stream. The temperature of the phosgene deficient stream is then decreased, and contacted with an adsorbent to remove the chlorine in the stream by adsorption to form a chlorine and phosgene free condensed stream. The chlorine and phosgene free stream is stripped using an inert gas to form a BCl 3  product condensed stream, and an inert gas is used to pump the BCl 3  product condensed stream to a product receiver.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to processes and systems for purifying borontrichloride. In particular, the invention relates to processes andsystems or apparatus which remove several critical impurities of borontrichloride to produce a highly purified final product required for someof its more stringent applications.

2. Related Art

Boron trichloride (also referred to herein as “BCl₃”) is a highlyreactive compound packaged as a liquid under its own vapor pressure of1.3 bar (130 kPa) absolute at 21° C. that has numerous diverseapplications. It is used predominantly as a source of boron in a varietyof manufacturing processes. For example, in the manufacturing ofstructural materials, boron trichloride is the precursor for chemicalvapor deposition (“CVD”) of boron filaments used to reinforce highperformance composite materials. BCl₃ is also used as a CVD precursor inthe boron doping of optical fibers, scratch resistant coatings, andsemiconductors. Some of the non-CVD applications of BCl₃ are reactiveion etching of semiconductor integrated circuits and refining of metalalloys. In metallurgical applications, it is used to remove oxides,carbides, and nitrides from molten metals. In particular, BCl₃ is usedto refine aluminum and its alloys to improve tensile strength.

Two of the most stringent applications for high purity BCL₃ involvesemiconductor and optical fiber manufacturing. In these industries thespecified impurity levels in BCl3 must be of the order of 1 ppm or lessin order to maintain product quality. In fact, the impurities in mostcommercially available BCl₃ are often present at levels over two ordersof magnitude beyond acceptable levels for these processes such as, forexample, air, CO₂, HCl, Cl₂, and COCl₂ (“phosgene”). Furthermore, inthese particular applications, any oxygen or oxygen containingimpurities (such as phosgene) in the BCl₃ are especially detrimental tothe manufacturing process due to the formation of certain oxidecompounds. Another class of detrimental impurities in BCl₃ for theseprocesses are metal containing impurities.

Geographically, BCl₃ is produced almost entirely in the United States.As of 1995, as much as 220 metric tons has been consumed in the UnitedStates where about 30% has gone into the production of boronreinforcement filaments, the remaining split primarily amongsemiconductor etching, Friedel-Crafts catalysis reactions, andintermediate use in pharmaceuticals. In comparison, Japan consumes 70metric tons which was all imported from the United States. In Japan,BCl₃ is used primarily in semiconductor etching and manufacture ofcrucibles for silicon ingots. Western European countries consumed onlyabout 5 metric tons. (Chemical Economics Handbook, October, 1996.)

The source cost of BCl₃ varies considerably per pound depending uponpurity grade and supplier. There is a strong incentive to purchase BCl₃domestically at a low cost and purify the material to stringentsemiconductor purity requirements of technically 1 ppm or less for thelight impurities.

After extensively searching the literature and patents, there appears tobe no production process technology to have been described or patentedregarding how to efficiently remove various impurities from borontrichloride by an integrated purification process technology comprisingseveral different functional chemical processes which are connectedsequentially and various impurities associated with boron trichlorideare removed sequentially and continuously.

The removal of some impuritites in BCl₃ has been disclosed previously.In particular, most publications have focused on how to remove phosgenefrom boron trichloride. This is because phosgene has similar vaporpressure to BCl₃ and hence becomes difficult to remove by simpledistillation. The previous methods for phosgene removal from BCl₃include electrical discharge, laser pyrolysis, fractional distillation,UV photolysis, and redox chemistry.

Although the individual methods aforementioned had indicated to be ableto reduce phosgene content in boron trichloride to a certain degree,these methods do have their drawbacks. For instance, the use ofelectrical discharge and laser pyrolysis is difficult to implement on alarger industrial scale without extensive equipment and capital costs,and therefore, the economics are not feasible. UV photolysis lackseffectiveness for phosgene removal to very low ppm levels. Further, thesimilarity of physical properties of phosgene and boron trichloridemakes phase separation by distillation and differential surfaceadsorption difficult to implement in a practical manner. It is alsoknown to use selective chemistry to remove phosgene from BCl₃. In thesemethods phosgene in the BCl₃ is allowed to oxidize molten metals such asmercury, copper, and titanium to form the corresponding metal chloridesand carbon monoxide. Although effective in removing phosgene, thisapproach presents problems with metal contamination, which isparticularly difficult due to the volatility of metal chlorides.

In view of all the drawbacks aforementioned, the preferred process ofremoving phosgene is by thermal decomposition via a catalyst with aspecified elevated temperature. For example, the phosgene decompositionon a preferably metal free carbonaceous catalyst was described by twoearlier publications. However, in each of these two cases, othertroublesome impurities were generated (chlorine in one case, andhydrogen chloride in the other) which require independent purificationsteps.

Another problem with known BCl₃ purification methods is the need toresort to vacuum generating devices or thermal heating of sourcematerial and associated handling systems to improve the rate of vaportransport through packed beds of adsorbents or catalytic materials. Inknown BCl₃ purification methods using packed beds such as the case ofcarbonaceous catalysts, there are significant pressure drops associatedwith packed beds when high volumetric flow rates are employed and goodsurface contact required. For many gases, this is not a problem. But,when it comes to BCl₃, material transport through such pressure dropsbecomes significantly hindered due to the BCl₃ liquid having only a 1.3bar vapor pressure at ambient temperature. Thus, maintaining reasonableflow rates through such devices requires some auxiliary means ofpromoting flow. Conventionally, flow throughput can be advanced byeither increasing upstream pressure or decreasing downstream pressure.Increasing upstream pressure can be done using commonly known techniquesof gravimetric feeding, mechanical pumping, or thermal heating of sourcematerial. However, in the specific case of producing high puritycorrosive gases like BCl₃, the reactive nature of BCl₃ makes themechanical devices undesirable requiring high maintenance and excessivecosts while providing low reliability and the increased likelihood ofcontamination of the BCl₃ by metallic impurities. Gravimetric feeding(in other words, elevating source material relative to the rest of thesystem) effectively promotes flow as only 2 meter height provides almost1 bar additional upstream pressure. However, this approach still suffersfrom the intolerable feature of requiring material transport through thesystem as entirely liquid phase instead of vapor phase. As a consequenceof liquid phase present in the system, excessive contamination of BCl₃by metallic impurities can occur from enhanced liquid phase corrosionmechanisms thereby degrading product purity with detrimental metallicimpurities.

One known method of increasing upstream pressure with vapor condensationdownstream is to heat the source material and all associated gashandling components to an isothermal temperature. The method is feasiblebut requires careful temperature control to assure uniform temperaturethroughout the system. Although feasible, this technique becomesdifficult to implement in practice especially for high capacityindustrial production.

Resorting to decreasing downstream pressure has its difficulties also.The simplest approach of mechanical pumping suffers from the sameproblems as in the upstream case. The use of simple low temperaturecondensation of BCl₃ downstream prevents the problems of mechanicalpumping but will lead to accumulation of metallic impurities in thefinal product collected hence degrading purity.

SUMMARY OF THE INVENTION

In the processes of the present invention, phosgene removal is performedby the preferred thermal decomposition route in a manner in which thedecomposition impurities are preferably continuously removed. Inaccordance with the present invention, low temperature condensation isutilized along with secondary inert gas stream such as He, N₂, or Ar. Inthis technique, as disclosed in further detail herein below, the BCl₃material is carried through the defined purification system alone with asecondary inert gas stream. The presence of such a gas stream havinghigher vapor pressure allows the overall system to be operated at higherpressures than that provided from BCl₃ vapor pressure alone. This ispreferably performed most simply by bubbling the inert gas through theliquid BCl₃ and flowing the mixed gas stream through the system, afterwhich the inert gas is easily separated from the purified BCl₃ productcollected.

A first aspect of the invention is a process of producing a BCl₃ vaporstream containing an inert gas selected from the group consisting ofhelium, argon, krypton, neon, xenon, or mixtures of one or more ofthese, from a lower purity BCl₃ source, the BCl₃/inert gas vapor streamhaving less than 10 ppm chlorine, less than 10 ppm phosgene, and lessthan 10 ppm each of light impurities including, but not limited to,nitrogen, oxygen, carbon dioxide, carbon monoxide, and hydrocarbons suchas methane, and less than 10 ppm of nonvolatile metal containingspecies. In one embodiment, using helium as the inert gas, the processcomprises injecting helium into a container of a lower purity BCl₃source having phosgene impurity to produce a vapor stream comprisingBCl₃, helium, and phosgene; decomposing a major portion of the phosgenein the BCl₃, helium, phosgene vapor stream by heating the vapor streamto a first temperature, in the presence of a first material, todecompose substantially all the phosgene to carbon monoxide andchlorine, to form a first intermediate vapor stream comprising BCl₃,helium, carbon monoxide, and less than 10 ppm phosgene; and adsorbing amajor portion of the chlorine in the first intermediate vapor stream ata temperature lower than the first temperature using a second material,thereby producing the BCl₃/helium vapor stream having less than lessthan 10 ppm chlorine, less than 10 ppm phosgene, and less than 10 ppmeach of the light impurities. In preferred processes of the invention,the first and second materials are substantially the same.

A preferred process embodiment in accordance with this aspect of theinvention is wherein the heating step comprises preheating the vaporstream comprising BCl₃, helium, and phosgene prior to the vapor streamcomprising BCl₃, helium, phosgene contacting the first material, whichpromotes phosgene decomposition.

A particularly preferred process embodiment in accordance with thisaspect of the invention is wherein the preheating comprises heatexchanging the first intermediate vapor stream with the vapor streamcomprising BCl₃, helium, and phosgene.

Preferably, the phosgene decomposition step occurs in the presence of acatalyst, the catalyst comprising materials selected from the groupconsisting of carbon-based materials, alumina-based materials,silica-based materials, and mixtures thereof Preferably, if carbon isused, it is selected from the group consisting of naturally occurringcarbon, carbon molecular sieve, or other synthetic carbonaceousmaterial. Alternatively, phosgene decomposition can be implemented inthe processes of the invention with other reactive elements such asboron, silicon, and various metals such as titanium or zinc, asdescribed in U.S. Pat. Nos. 3,037,337; 3,043,665; and 3,207,581;however, such elements are not catalytic as they are consumed in theprocess, and are thus subject to depletion, thus they are not thereforethe preferred materials for the phosgene decomposition step.

In accordance with this aspect of the invention, the inert gas functionsto increase pressure of the vapor stream comprising BCl₃, inert gas, andphosgene to a pressure substantially higher than the vapor pressure ofthe lower purity BCl₃.

Preferably, the phosgene decomposition step occurs at a temperaturegreater than about 200° C., and the adsorption of chlorine steppreferably occurs at a temperature lower than about 50° C., althoughsome chlorine will be adsorbed on the first material at a highertemperature in the phosgene decomposition step.

Furthermore, the chlorine adsorption step preferably comprises using abed of adsorbent until loaded, removing the bed of adsorbent, heatingthe removed bed of adsorbent, and reinstalling the bed. More preferably,a second chlorine adsorption bed of same or different adsorbent could beutilized while the first is regenerating, in order to maintaincontinuity of the process. Alternatively, but less preferable, is theuse of one bed of chlorine adsorbent with the appropriate valveconfiguration to allow isolation from the process and conduit connectionto a regeneration system, be it via heated purge or vacuum induceddesorption.

A second aspect in accordance with the invention is a process forproducing an ultra-pure BCl₃ condensed phase from a vapor phasecomprising impure BCl₃. The process comprises condensing a first vaporstream in a condenser, the first vapor comprising a major portion ofBCl₃ and a minor portion of HCl, light impurities, and a first inert gasselected from the group consisting of helium, argon, krypton, neon,xenon, and mixtures thereof, to form a first condensed phase comprisingBCl₃ and a second vapor comprising the first inert gas, BCl₃, and lightimpurities; routing the second vapor stream to a secondary condenser, ata lower temperature, thus forming a gaseous stream containing HCl, lightimpurities, and the first inert gas and a second condensed phasecomprising BCl₃; and routing the first condensed phase to a stripper, orusing the condenser itself at a more optimal temperature, wherein asecond inert gas (the same as or different from the first) is used tostrip molecules having vapor pressure greater than BCl₃ from the firstcondensed phase to produce a higher purity first condensed phase havingless than 50 ppm hydrogen chloride, preferably less than 1 ppm hydrogenchloride, and a stripped vapor phase.

Preferably, the stripping step includes the step of allowing the firstcondensed phase to come to room temperature, and then contacting it withhelium at a pressure ranging from about 20 psig to about 30 psig [fromabout 240 kPa to about 440 kPa].

Also, preferred are processes in accordance with this aspect wherein thestripped vapor phase is routed to the secondary condenser to recoverresidual BCl₃, and processes wherein the stream containing only tracesof BCl₃ from the secondary condenser is routed to a scrubber to removeresidual traces of BCl₃, along with HCl impurity and introduce a gaseousstream containing the inert gas and light impurities which aredischarged to the atmosphere.

Further preferred processes in accordance with this aspect are thosewherein the higher purity first condensed phase is transferred to aproduct container using ultra-high purity inert gas, preferably heliumand without any other pumping or vacuum means.

A third aspect of the invention is a process for producing ultra-highpurity boron trichloride in condensed phase from a lower purity borontrichloride condensed phase having phosgene impurity, the processcomprising injecting an inert gas, preferably helium, into a containerof lower purity BCl₃ liquid having phosgene impurity to produce a vaporstream comprising BCl₃, inert gas, and phosgene; decomposing a majorportion of the phosgene in the BCl₃, inert gas, phosgene vapor stream byheating to a first temperature to form a first intermediate vapor streamcomprising BCl₃, inert gas, carbon monoxide, chlorine and less than 10ppm phosgene; adsorbing a major portion of the chlorine in the firstintermediate vapor stream at a temperature lower than the firsttemperature using a solid adsorbent material, thereby producing theBCl₃/inert gas vapor stream having less than 10 ppm phosgene and lessthan 10 ppm Cl₂; routing said BCl₃/insert gas vapor stream having lessthan about 10 ppm phosgene and less than 10 ppm Cl₂ to a condenser;condensing a first vapor stream in the condenser, the first vaporcomprising a major portion of BCl₃ and a minor portion of HCl, inertgas, and light impurities to form a first condensed phase comprisingBCl₃ and a second vapor comprising the inert gas, residual BCl₃, andlight impurities; routing the second vapor stream to a secondarycondenser, thus forming a gaseous stream containing only traces of(preferably less than about 10 ppm) BCl₃ and a second condensed phasecomprising BCl₃; and routing the first condensed phase to a stripper (orusing the secondary condenser itself at a more optimal temperature)wherein inert gas (preferably ultra-pure helium) is used to stripmolecules having a vapor pressure greater than BCl₃ from the firstcondensed phase to produce a higher purity first condensed phase havingless than 50 ppm HCl, preferably less than 1 ppm HCl, and a strippedvapor phase.

A fourth aspect of the invention is a process for increasing thecondensed phase production of BCl₃ having less than about 10 ppmphosgene, less than about 10 ppm chlorine, less than about 10 ppm eachof light impurities, and less than about 10 ppm HCl, the processcomprising the steps of: introducing an inert gas selected from thegroup consisting of helium, argon, neon, xenon, krypton, and mixturesthereof into a container having condensed BCl₃ therein, the condensedBCl₃ having therein a minor portion of phosgene impurity; converting amajor portion of the phosgene in the condensed BCl₃ to carbon monoxideand chlorine by increasing temperature of the condensed BCl₃; decreasingthe temperature of the stream and removing the chlorine by adsorptionand the carbon monoxide by stripping with an inert gas selected from thegroup consisting of helium, argon, xenon, krypton, neon, and mixturesthereof (preferably helium); and using the inert gas to transfer theBCl₃ product to a product container.

In accordance with the present invention, several of the problemsencountered in the prior art methods are overcome in the processes andapparatus of the present invention. By use of the inventive purificationprocess technology, all significant impurities of interest in BCl₃ forsuch high purity applications as semiconductor and fiber opticmanufacturing are removed in the inventive processes such that a lowpurity boron trichloride now can be purified into an ultra-pure productwith a purity of 99.9995% or higher (on a helium-free basis), or higherrequired for certain semiconductor and fiber optic manufacturing. Theinventive processes and apparatus are preferably designed so as tominimize capital investment costs and to improve reliability. Inaddition, environmental emission is minimal, thereby reducing exhaustabatement requirements and increasing product yield. The inventivechemical process technology is composed of several different functionalchemical processes or operating units as listed in the following:

Injecting an inert gas, preferably helium, into a source container oflower purity BCl₃ liquid and extract the vapor out the container;

Using a functional catalyst such as activated carbon to thermallydecompose phosgene at elevated temperature;

Using an adsorbent such as activated carbon to remove remaining chlorineat 50° C. or lower;

Condensing BCl₃ vapor which has substantially less phosgene and chlorinethan the source BCl₃;

Using an inert gas to strip the BCl₃ liquid to remove carbon monoxide,carbon dioxide, hydrogen chloride, nitrogen, oxygen and other lightergas impurities that may be associated with lower purity BCl₃ at thebeginning, and/or generated during phosgene and chlorine removingprocesses upstream.

Transfilling the final BCl₃ product from the inventive system into theproduct storage container using inert gas pressure and no other pumpingor vacuum means.

It has been demonstrated that the inventive process technology is fullycapable of producing an ultra-pure BCl₃ product due to the followingimportant new features.

Activated carbon is a particularly preferred material for the catalyticand adsorption steps, used both at high and low temperatures in such away as to decompose phosgene and adsorb chlorine byproduct,respectively. One aspect that is surprising and unexpected in thepresent invention is that the carbon monoxide and chlorine byproducts ofphosgene decomposition can be introduced into a lower temperature carbonbed without reformation of phosgene under the process conditionspresented. The preferred activated carbon material was found to be fullyregenerable to chlorine adsorption without degradation inactivity fromBCl₃. The preferred activated carbon catalyst which decomposes phosgenehas shown the function of a catalyst at the elevated temperature, andtherefore, the carbon can be continuously used without addressing theconcern of saturation and regeneration.

An ultra-dry inert gas such as helium is employed in the inventiveprocess technology which overcomes the problem of BCl₃'s low vaporpressure, and the inert gas can drag BCl₃ vapor out of the low puritycontainer and carry the vapor through different purification processunits. As a result, this process totally eliminates the requirement ofheating the lower purity BCl₃ liquid in order to provide enough vaporpressure penetrating each production process unit and of maintaining anisothermal operating condition in order to avoid the vapor condensationwhere the recondensation is not desired.

Further, the BCl₃ purification processes and systems of the presentinvention do not require any mechanical devices either to transfer thelow purity BCl₃ into the purification system, or to transfill the finalhigh purity product BCl₃ from the inventive system into a storagecontainer. The potential contamination on the final high purity productBCl₃ by mechanical transfer means is therefore preferably eliminated,and consequently, the inventive processes and systems also operate moredependably and reliably because no mechanical component is involved inthe transfer process.

In addition, the inventive processes and systems are able to run thevapor condensation and the liquid stripping separately, orsimultaneously. Each chemical process unit operation of the inventiveprocesses is preferably connected sequentially and the impuritiesremoval operating is preferably continuously. The operating processminimizes potential air contamination and effects thereof because theentire process can be done without breaking down the system exceptchanging the low purity and product containers. Besides, the productionprocesses of the invention are very economical due to the productrecovery from the process being 99.99% or higher within the secondarycondenser, and consequently, this process technology is environmentallynonintrusive because the product is almost totally recovered withremaining trace BCl₃ and HCl impurity easily removed by conventionalscrubber technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents in schematic format an apparatus and process inaccordance with the present invention; and

FIG. 2 represents in schematic format the apparatus and process of FIG.1, emphasizing certain details of the inventive apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a preferred system 1 of the invention includes alow purity BCl₃ source container 2 and first and second valves 6 and 8which together form a dual valve T assembly which is sealed into sourcecontainer 2, as further described in the examples. A tube 5 extends fromthe bottom of valve 6 into source container 2; an exterior port of valve6 is connected to a valve 10. Valve 10 in turn is connected to a conduit12 leading to a source 20 of inert gas, for example helium. A secondvalve 14 and another conduit 16 also connect to the helium source 20 aswell as a third conduit 18 which leads to conduit 22 and other parts ofthe apparatus. A connection off conduit 24 leads to a scrubber unit,while conduit 24 itself leads to a valve 26 and conduit 28 which itselfleads to a heat exchanger 27. Heat exchanger 27 represents a positiveheat flow (preferably from heat exchange with flow of hot vapor exitinga reactor 30) into a low purity BCl₃/helium mixture emanating from lowpurity BCl₃ source container 2. An electrically heated furnacesurrounding the reactor supplies supplemental heat input into reactor 30as required. The low purity BCl₃/helium mixture passes through conduit28 and heat exchanger 27 and enters phosgene decomposition reactor 30preferably from the bottom, although this is not necessary. Thesubstantially “phosgene free” boron trichloride vapor having heliumtherein is directed through a conduit 32, valve 36, conduit 38, andanother heat exchanger 37 which removes heat from the substantiallyphosgene free mixture before flowing into a chlorine adsorption unit 40,where an effective amount of an adsorbent is packed for chlorineremoval. As with heat exchanger 27, heat exchanger 37 can be any type ofa variety of heat exchanger designs, such as shell and tube, tube andtube, cooling fins attached outside of conduit 38, or even spiral woundheat exchangers. In any case, chlorine adsorption unit 40 is plumbedthrough a conduit 44 and a valve 46, a conduit 64, and a valve 72, intoa condenser 50. A valve 34 and a conduit 42 are provided for bypassingof chlorine adsorption unit 40 if it is not needed as further explainedherein. A valve 48 allows for introduction of additional helium pressureflow into the system. A conduit 52, a valve 54, and a conduit 56 may beused to take a product stream from the system of the invention. A valve58 and another conduit 62 preferably lead to the analytical systems suchas FTIR and UV analyzers.

Condenser 50 is fitted with a dual valve T formed from valves 72 and 74,valve 72 having a dip tube 55 extending into condenser 50, preferably asillustrated in FIG. 1. After a substantial portion of the borontrichloride vapor is liquefied in condenser 50, the gas in line 76 maystill contain boron trichloride vapor. This vapor is routed to asecondary condenser 60 through valve 82 to dip tube 65. Valves 82 and 84form another dual valve T assembly. A conduit 78 and a valve 86 form abypass around secondary condenser 60. Any non-condensed BCl₃, in theflow exiting condenser 60, is routed to a conduit 88, a conduit 94, anda valve 92 followed by to a scrubbing unit. A valve 90 allows heliumfrom source 20 and conduit 18 to force vapor through the scrubber.

Referring now to FIG. 2, some details of one preferred apparatus areexplained in further detail. Where numerals appear as first indicated inFIG. 1, those numerals are equivalent to those in FIG. 2. Thus, FIG. 2illustrates phosgene decomposition reactor 30, and chlorine adsorptionunit 40. Conduit 44 leading out of chlorine adsorption unit is shown inthis figure to lead to a filter 63 which removes particles which mayhave been carried over from the phosgene decomposition reactor 30 and/orthe chlorine adsorption unit 40. Filter 63 is connected to a conduit 64,valve 72, and dip tube 55, and into condenser 50. Condenser 50 isvertically positioned in a vacuum jacketed top sealed container 100, andis typically and preferably surrounded by a liquid nitrogen cooling coil102. Both condenser 50 and cooling coil 102 are immersed in a heattransfer medium 104, such as an alcohol liquid bath. Liquid nitrogenenters the cooling coil through conduit 126 to exchange heat with theliquid bath and container 100. Gaseous nitrogen or a mixture of gaseousnitrogen and liquid nitrogen exits through conduit 128. As will beapparent to the skilled artisan, other low temperature fluids may servethis purpose as well, such as liquid argon.

Referring again to FIG. 2, illustrated is a conduit 106, exiting fromcontainer 100, leading to a stripper column 120. Stripper column 120 hasa source of helium, typically entering at the lower end of column 120through a conduit 108. This helium flows up the stripper column, andexits with some trace level BCl₃ vapor and other impurities throughvalve 101 and conduit 103, and leads preferably to another vacuumjacketed top sealed container 110 having therein secondary condenser 60.Secondary condenser 60 is surrounded with a liquid nitrogen cooling coilwhere liquid nitrogen enters through a conduit 130 and either a gaseousnitrogen, or a combination of liquid and gaseous nitrogen exits. Vacuumjacketed and top sealed container 110 contains a heat transfer bath 112and both coil 114 and secondary condenser 60 are immersed in the heattransfer fluid 112 contained in container 110.

Both the vacuum jacketed and top sealed container 100 and 110 have ventsystems. As depicted in FIG. 2, container 100 has a vent conduit andvalve 71 and 73 leading to a scrubber, while container 110 has a ventconduit 81 and valve 83 also leading to a scrubbing unit. Strippedproduct is removed from stripper 120 via conduit 116 and valve 118. Theoperation of the various inventive apparatus depicted in FIGS. 1 and 2are now explained in further operational detail using helium as theinert gas.

Helium with a pressure ranging from about 150 to about 250 psig (about1130 to about 1820 kPa) from source 20 has been previously directed intoa molecular sieve bed (not illustrated) for trace moisture removal.Hence source 20 is a supply of ultra-dry helium (simply referred to ashelium hereinafter). The ultra-dry helium stream is then preferablybranched to one or more different processing operations with anindividually specified pressure. Helium from source 20 has also passedthrough a gas filter (not illustrated) where particles with a size of0.003 μm or larger were removed.

One helium flow, with a pressure ranging from about 20 to about 30 psig(about 240 to about 310 kPa), is directed via dip tube 5 into the lowpurity boron trichloride liquid container 2 and bubbles through the lowpurity BCl₃ liquid where a mixture of the helium and BCl₃ vapor isgenerated. This mixture is carried into the phosgene decompositionreactor 30 in which an effective amount of catalyst, preferablyactivated carbon, is packed. The phosgene, as one of the impuritiesassociated with low purity boron trichloride, is decomposed into CO andCl₂ with the help of the catalyst at an operating temperature rangingfrom about 480 to about 700° F. (250 to 370° C.). Reactor 30 is heatedby an electric furnace surrounding the reactor. Within reactor 30, anelevated phosgene concentration of 500 ppm or higher in the low purityBCl₃ can be reduced to less than 0.1 ppm. In a laboratory setting, thesuperficial residence time was about 1 second in reactor 30. Due to thefact that the activated carbon functions as a catalyst, saturation ofthe activated carbon is not a concern in this technology.

Then “phosgene free” boron trichloride vapor mixed with the helium isdecreased in temperature to between 50 to 80° F. (10 to 26° C.) by heatexchange with air. The cooled gas is then directed into adsorption unit40 where an effective amount of activated carbon is packed mainly forthe purpose of chlorine removal. Since CO and Cl₂ can reform intophosgene at slightly elevated temperature, it is imperative to reducethe temperature to less than about 80° F. (26° C.) prior to directingthe phosgene free BCl₃ into the second low temperature adsorbent unit 40and maintain this low temperature in order to prevent reformation ofphosgene. Further since both Cl₂ adsorption and reformation of phosgeneare exothermic reactions, adsorption unit 40 is preferably configured toprevent substantial temperature build-up in adsorption unit 40. Byexperiments, the preferred catalyst, activated carbon, used inadsorption unit 40 has chlorine adsorption capacity of 20%. Adsorptioncapacity less than 20% is considered within the invention, but it shouldbe at least 10% to be practical. In other words, one pound (454 grams)of the preferred activated carbon can preferably retain 0.2 pound (91grams) of chlorine. By this unit operation, the generated chlorine canbe reduced to 1 ppm or less in the BCl₃ stream. The preferred activatedcarbon can be regenerated by heating the bed for a time sufficient todrive off the adsorbed chlorine.

Either the phosgene decomposition reactor 30 or chlorine adsorption unit40 may contribute particles into the boron trichloride stream due to thefact that both are packed preferably with a granular material.Therefore, the flow stream exiting chlorine adsorber unit 40 preferablypasses through a filter 63 in which particles having a size of 0.003 μmor larger will be retained.

After the particles are removed, the stream is then passed into acondenser 50 through a dip tube 55. The temperature of condenser 50 iscontrolled between −80 and −100° F. (−62 and −73° C.) thus causing themajority of the boron trichloride vapor to be liquefied and stored.Condenser 50 is preferably vertically positioned in a vacuum jacketedtop sealed container 100 (more fully described in reference to FIG. 2)in which condenser 50 is surrounded by a liquid nitrogen cooling coil102. Both condenser 50 and cooling coil 102 are immersed in a heattransfer medium 104 such as an alcohol liquid bath.

The alcohol liquid bath 104 is refrigerated and maintained at adesignated condensation operating temperature by liquid nitrogen passingthrough coil 102. After the boron trichloride vapor is liquified incondenser 50, the helium flow exiting from condenser 50 in line 76 maystill contain between 0.5 and 1.5% of boron trichloride vapor, theactual amount depending upon operating parameters typically used byskilled artisans. This vapor is routed to a secondary condenser 60through valve 82 and dip tube 65 for further boron trichloride vaporcollection where the operating temperature is preferably controlled atbetween −120 and −125° F. (−84 and −87° C.). The configuration andarrangement of secondary condenser 60 are similar to condenser 50 exceptfor the lower operating temperature. Secondary condenser 60 is cooled bycooling coil 114. Both coil 114 and secondary condenser 60 are immersedin a heat transfer bath 112 contained in vacuum jacketed, top sealedcontainer 110. The BCl₃ concentration in the effluent from secondarycondenser 60 through valve 84 and conduit 88 is less than 100 ppm. Thiseffluent is directed to a scrubber through valve 92 and conduit 94. Oncethe BCl₃ liquid level inside condenser 50 reaches the designated holdingcapacity, the cold liquid BCl₃ then is preferably totally transferredvia line 106 into the stripper column 120 by the helium for furtherimpurities removal.

After the BCl₃ liquid in stripper 120 has warmed up to room temperature,the BCl₃ liquid is stripped by the helium entering at conduit 108 at anoperating pressure ranging from about 20 to about 30 psig (about 240 toabout 310 kPa) to strip the gas impurities out of the BCl₃ liquid. Thestripped-out flow stream in line 103 is comprised of carbon monoxide,carbon dioxide, nitrogen, oxygen, hydrogen chloride, and other light gasimpurities along with BCl₃ entrained in helium. The stripped-out flowcontaining BCl₃ vapor is directed into secondary condenser 60 forfurther BCl₃ vapor recovery by opening valve 101. The effluent streamfrom secondary condenser 60 in conduit 94 and valve 92 is neutralized bya wet chemical scrubber (not shown) to remove trace BCl₃ vapor and otheracid components such as HCl before final discharge to atmosphere.

The stripping operation in stripper 120 is continued for a length oftime depending upon the starting impurity concentration and the finalproduct specification requirements. This process can reduce theconcentrations of carbon monoxide, carbon dioxide, nitrogen, and oxygento less than 0.1 ppm in gas phase. One more important accomplishment isthat this process is able to reduce hydrogen chloride to 1 ppm or lowerin gas phase.

Once the concentrations of the impurities meet the final productspecifications, the product is pushed out from the purification systemvia conduits 116 and 122 and valves 118 and 124 into a product container(not shown) by helium. Stripper 120 is then ready for another strippingoperation while the vapor condensation is continued in condenser 50.

EXAMPLES Example 1

In this example, the BCl₃ source container 2 was an approximately 50liter carbon steel storage vessel that was equipped with a “dual valvetee” at one end. “Dual valve tee” refers to two valves connected to atee union whereby the base of one valve has a dip tube extending intothe vessel.

The dual valve tee design was used in order to introduce He (at a fewguage pressure) into the liquid port valve 6 and withdraw resultant Heand BCl₃ vapor mixture from the vapor port valve 8 In this way He, ineffect, bubbled directly through the liquid phase of BCl₃ carryingprimarily BCl₃ vapor into the purification system. When using He in thismanner no recondensation of BCl3 was observed inside the processing oranalytical systems even though ambient temperature vapor pressure isonly 1.3 bar.

High purity He and N₂ were used for inert gas purging where needed. Theinlet to the exhaust scrubber system was a water venturi drawing avacuum of about 20 inches Hg (50 cm Hg) (gauge pressure). This vacuumsource was also available at various points along the purification trainto allow removing of BCl₃ vapor from the conduits. As a precautionarymeasure, the He line had a molecular sieve drier placed upstream toprevent any moisture contamination from the He source. Such moisturewould react with BCl₃ to form boric acid (a solid) and HCl. The drierturned out to be highly preferred because in one set of tests moisturecontamination was present in some of the helium delivery lines. Theresultant moisture contamination in this case lead to formation of HClat high ppm levels; the additional HCl formation was eliminated uponinstallation of the drier.

After the He BCl₃ vapor mixture left the source container 2, it entereda phosgene decomposition reactor 30, which decomposed the COCl₂impurity. This tubular reactor was arranged vertically in a clam shellfurnace with flow entering the bottom of the reactor. The temperature ofreactor 30 was controlled at 350° C. by means of an external electricalheater. The reactor 30 contained 8.5 lbs. (about 4.2 kg) of BPL 4×6granular activated carbon from Calgon. The reactor had dimensions of 4inches (10 cm) in diameter and 36 inches (about 90 cm) in length. Priorto use, the activated carbon was extensively dried by a heated N₂ purgefor several weeks.

After passing through the phosgene decomposition reactor 30, the He BCl₃mixture with some CO and Cl₂ passed through some intermediate 0.5 inch(1.27 cm) stainless steel tubing wrapped with thin metal heat transferfins and a tube-in-tube heat exchanger before entering the chlorineadsorption unit 40. The fins and heat exchanger were needed for twopurposes, to reduce the temperature of the He/BCl₃/Cl₂/CO gas streamexiting reactor 30 so valves in the system were not destroyed by thehigh heat, and to prevent heating of the chlorine adsorption unit 40,which can lead to reformation of COCl₂. The unit 40 was much smaller insize than reactor 30 and was oriented horizontally. It containedapproximately 0.2 lbs. (0.1 kg) of the same activated carbon as reactor30. The unit 40 was used to remove any chlorine generated and thenreleased from reactor 30. In performing Cl₂ analysis after the carbonbeds 30 and 40, it was observed that initially all the Cl₂ was absorbedby reactor 30 alone. Eventually, when reactor 30 became saturated withCl₂, breakthrough occurred. The released Cl₂ was then removed byadsorption unit 40.

After passing through adsorption unit 40, the BCl₃ was transferredtowards two low temperature condensers 50 and 60 maintained at twodiffering sub-ambient temperatures. Condensers 50 and 60 were equivalentin size to BCl₃ source vessel 2. Both condensers had dual valve tees andwere plumbed in series, with gas entering the inner tube of the firstcondenser 50 and exiting to the inner tube of the second condenser 60.The first condenser 50 was contained in a dewar 100 with a glycolsolution cooled by a refrigeration unit. The temperature of the cylinderwas controlled from −11 to 40° C. During purification runs, the glycolsolution was typically at about −5° C. The second condenser 60 was alsocontained in a dewar 110 which was packed in dry ice (about −78° C.).

FTIR and UV analyzers were installed to allow sampling of gas from manypoints in the purification system. Sampling of source BCl₃ was done bydirectly connecting BCl₃ source container 2 to the FTIR/UV analyticalsystem. Gas flow exited the analytical system directly to the scrubber(not shown).

Design of the scrubber proved to be a fairly daunting task because ofthe properties of BCl₃ . Its relatively low vapor pressure at roomtemperature (about 1.3 bar, or about 130 kPa) causes it to vaporize veryslowly. This combined with the fact it forms a solid (boric acid) uponcontact with moisture caused a lot of problems with clogging of thescrubber lines. The original scrubber system used for this study was aconventional wet scrubber for acid gases. The input lines had a waterventuri system with a flow rate of about 4 gallons/min (about 17.6liters/min) which recirculated from scrubber to venturi. The venturicreated a vacuum of about 20 inches Hg (about 51 cm Hg). This set-up wasespecially effective for hydroscopic gases like HBr or HCl that readilydissolve in water. BCl₃, however, forms solid boric acid on contact withwater. This lead to plugging problems and the scrubber design had to beslightly modified.

Modification of the scrubber was made in order to alleviate suchproblems described above. In order to allow the BCl₃ to dissolve in thewater yet avoid contact with moisture vapor in the sampling lines, a twoliquid phase system involving a halocarbon oil and sodium hydroxidesolution was used. The halocarbon oil, having a density greater thanwater, settles on the bottom of the scrubber container. The gas streamto be treated is then directed to the bottom of the oil layer afterwhich it bubbles up to an aqueous sodium hydroxide layer and reacts. Theaqueous sodium hydroxide layer is typically a 3-6% by weight solution ofNaOH. In one case experiment, this halocarbon-aqueous scrubber wasplaced just prior to the venturi inlet of the conventional acid scrubberunit. The vacuum created by the venturi was reduced in order to preventany rapid evaporation of the NaOH solution from the two-phase unit. Theuse of the halocarbon-aqueous scrubber greatly reduced plugging of theconventional acid scrubber system.

All of the conduits used in the purification system were made of 0.25inch (0.635 cm) and 0.5 inch (1.27 cm) diameter 316L SS electropolishedtubing while some of the FTIR sampling lines were 0.125 inch (0.317 cm)316L SS. Actual flow rates were determined by tracking weight loss ofthe source container 2 and the weight increase of the collectioncylinders (not shown) over time.

Analysis and Calibrations The FTIR used was a Midac FTIR configured tooperate at 2 cm⁻¹ resolution with a MCT detector. It had an Axiom foldedpath gas cell with an effective path length of 4 meters. Prior to thisstudy, calibration of the FTIR was done for COCl₂, HCl, and CO.

TABLE 1 Calibration of the FTIR using various gas standards Cell PeakConcen- Pressure Location Peak Height tration Detection Impurity (psig)(cm−1) (Abs units) (ppm) Limit (ppm) COCl₂ Near  851 0.422 23 ˜0.1 (balN₂) ambient pressure HCl 5 3014, 2998 0.038, 0.051 50 ˜0.5 (bal N₂) CO 52172 0.044 50 ˜0.5 (bal N₂)

For HCl, the peaks analyzed were at 2998 cm⁻¹ and 3014 cm⁻¹. These peakswere chosen since they did not interfere with the large BCl₃ peakslocated within the HCl band. The estimated noise level provideddetection limits of approximately 0.5 ppm under these experimentalconditions.

For CO analysis, the peak at 2172 cm⁻¹ was chosen. There is aninterference with BCl₃ throughout the entire CO band. However, this wasnot a problem for the analysis of CO since the line width of the BCl₃peak is much broader than the line width of the CO peaks. A simplesparging with He effectively reduced the CO below the detection limit of0.5 ppm under these experimental conditions.

For Cl₂ analysis, a UVNIS spectrometer (Ocean Optics) with afiber-coupled one-meter gas cell was utilized. The purpose of thisanalysis was to make sure no Cl₂ from COCl₂ pyrolysis remained in thepurified product. Calibration of this instrument was performed usingCl₂/N₂ mixtures. No Cl₂ was seen in the purified product during theseinitial purification runs even though Cl₂ was formed from the phosgenedecomposition. This is believed to be due to the high adsorptionefficiency of the carbon used in the set up.

During analysis with FTIR or UIVIS, the concentration of BCl₃ in theHe/BCl₃ mixture varied from day to day somewhat due to resultingtemperature of source BCl₃. This was due to variations of both ambienttemperature (changing the vapor pressure of BCl₃) and the flow rate ofhelium (helium flow rate is not controlled only helium pressure). Inorder to determine the BCl₃ concentration when helium was present, aweak BCl₃ band at 2139 cm⁻¹ was measured. By monitoring this peak andcomparing to that from 100% BCl₃, a determination of the BCl₃concentration was estimated. Typically, BCl₃ level was around 60-70%.

Preparation of System

The activated carbon beds were dried down with a N₂ purge at theoperating temperature of350° C., and above, for several weeks prior totheir first exposure to BCl₃. At no time during the pilot scale trialswere the carbon beds purged with either helium or nitrogen. BCl₃ is leftstagnant in the trap between purification runs. This is basicallykeeping the system free of outside impurities, particularly tracemoisture, that will exist in the purge gas at low levels. It alsominimized the loss of any BCl₃ during purification. After more than sixmonths of operation, the same carbon was still being used in reactor 30without any noticeable degradation in performance.

Example 2

In this case, the source container was replaced with a larger unitcontaining approximately 1200 lbs. (600 kg) of BCl₃. This container waspositioned horizontally offering larger liquid-vapor interface area andin this example the inner tube of the container had a dip tube thatallowed He to flow directly through the liquid BCl₃ and out a secondvalve of the vapor phase portion of the container into the purificationtrain. In this modification of the system, the process procedure was thesame as in Example 1 except additional helium was injected into the lowtemperature condensers by feeding He in just after the second (lowtemperature) carbon bed and thus having it flow through the twocondensers and out the scrubber like a normal purification run. Thisadditional injection of helium lowered the CO and HCl impurities down todetection limits of 1 ppm or less.

Subsequent gas chromatography analysis indicated no light impuritieswere present in the purified BCl₃ above a detection limit of 100 ppbfrom current or previous purification work.

Based on the current limited sampling results available today, theconcentration level of metals falls within the range of that measuredfrom a competitive high purity BCl₃ supplier even though the inventivesystem did not have any secondary vaporization process specifically forremoving metals. Even so, typically, the level of metals (whether fromsamples produced by inventive system or the competitive high purity BCl₃sample) fall around a few to tens of ppb level for most elements. Veryoften the most abundant impurity elements found in BCl₃ from either theinventive system or the competitive high purity BCl₃ sample are Fe, Ca,and Si. These analysis results are taken with liquid phase samplingfollowed by residue analysis.

Overall, the BCl₃ purification process and system of the presentinvention was a success and high purity BCl₃ required for existingsemiconductor manufacturers is obtained from low purity BCl₃. The maingoal of this invention was to take low purity BCl₃ with ˜100 ppm ofCOCl₂ and produce pure product meeting today's typical semiconductorspecifications.

While reference has been made to specific embodiments, these are onlymeant to be illustrative and those possessed of ordinary skill in theart may alter such embodiments without departing from the scope of theappended claims.

What is claimed is:
 1. A process of producing a BCl₃/inert gas vaporstream from a low purity BCl₃ source, the BCl₃/inert gas vapor streamhaving less than 10 ppm chlorine and less than 10 ppm phosgeneimpurities, the process comprising: a) injecting an inert gas into acontainer comprising low purity BCl₃ having phosgene impurity and avapor pressure to produce a vapor stream comprising BCl₃, inert gas, andphosgene; b) decomposing a major portion of the phosgene in the vaporstream comprising BCl₃, inert gas, and phosgene by heating to a firsttemperature to form a first intermediate vapor stream comprising BCl₃,inert gas, carbon monoxide, chlorine and less than 10 ppm phosgene; andc) adsorbing a major portion of the chlorine in the first intermediatevapor stream at a temperature lower than the first temperature using asolid adsorbent material, thereby producing said BCl₃/inert gas vaporstream having less than 10 ppm chlorine and 10 ppm phosgene.
 2. Aprocess in accordance with claim 1 wherein said heating step comprisespreheating the vapor stream comprising BCl₃, inert gas, and phosgene andthen contacting the preheated vapor stream comprising BCl₃, inert gas,and phosgene with a catalytic material.
 3. A process in accordance withclaim 2 wherein said preheating comprises heat exchanging said firstintermediate vapor stream with said vapor stream comprising BCl₃, inertgas, and phosgene.
 4. A process in accordance with claim 1 wherein saidphosgene decomposition step occurs in the presence of a catalyst.
 5. Aprocess in accordance with claim 4 wherein said catalyst is selectedfrom the group consisting of carbon-based material, alumina-basedmaterial, silica-based material, or mixtures thereof.
 6. A process inaccordance with claim 5 wherein said carbon-based material is selectedfrom the group consisting of naturally occurring carbon, carbonmolecular sieve, synthetic carboneous material which is not molecularsieve, and combinations thereof.
 7. A process in accordance with claim 1wherein said inert gas increases pressure of the vapor stream comprisingBCl₃, inert gas, and phosgene to a pressure substantially higher thanthe vapor pressure of the low purity BCl₃.
 8. A process in accordancewith claim 1 wherein the phosgene decomposition occurs at a temperaturegreater than about 200° C., and the adsorption of the chlorine occurs ata temperature lower than about 30° C.
 9. A process in accordance withclaim 1 wherein said adsorption step comprises using a bed of adsorbentuntil loaded, isolating the bed from the first intermediate vaporstream, heating the isolated bed for a time and at a temperatureeffective to desorb substantially all chlorine, and reusing the bed. 10.A process in accordance with claim 1 wherein said adsorbent is selectedfrom the group consisting of carbon-based material, alumina-basedmaterial, silica-based material, and mixtures thereof.
 11. A process inaccordance with claim 10 wherein said carbon-based material is selectedfrom the group consisting of naturally occurring carbon, carbonmolecular sieve, synthetic carboneous material which is not molecularsieve, and combinations thereof.
 12. A process in accordance with claim1 wherein the catalyst and the adsorbent each comprise carbonaceousmaterial.
 13. A process for producing an ultra pure BCl₃ condensed phasefrom a vapor phase comprising BCl₃, the process comprising: a)condensing a first vapor stream in a condenser, the first vapor streamcomprising a major portion of BCl₃ and a minor portion of HCl and aninert gas to form a first condensed phase comprising BCl₃, and a secondvapor stream comprising the inert gas, BCl₃, and light impurities; b)routing the second vapor stream to a secondary condenser, thus forming agaseous stream containing less than 10 ppm of BCl₃ and a secondcondensed phase comprising BCl₃; and c) routing the first condensedphase to a stripper wherein an inert gas is used to strip moleculeshaving specific gravity less than BCl₃ from the first condensed phase toproduce a third condensed phase having less than 50 ppm hydrogenchloride, and a stripped vapor phase.
 14. A process in accordance withclaim 13 wherein step (c) includes the step of allowing the firstcondensed phase to come to room temperature, and then contacting thefirst condensed phase with inert gas at a pressure ranging from about 20psig to about 30 psig.
 15. A process in accordance with claim 13 whereinthe stripped vapor phase is routed to the secondary condenser to recoverresidual BCl₃.
 16. A process in accordance with claim 13 wherein thegaseous stream containing less than 10 ppm BCl₃ from the secondarycondenser is routed to a scrubber to neutralize the BCl₃ in the gaseousstream containing less than 10 ppm BCl₃, and produce a gaseous streamcontaining nitrogen and oxygen.
 17. A process in accordance with claim13 wherein the third condensed phase is transferred to a productcylinder using ultra high purity inert gas and without any other pumpingmeans.
 18. A process for producing ultra-high purity BCl₃ in condensedphase and containing less than 10 ppm phosgene from a low purity BCl₃condensed phase having phosgene impurity, the process comprising: a)injecting an inert gas through a low purity BCl₃ having phosgeneimpurity to produce a vapor stream comprising BCl₃, inert gas, andphosgene; b) decomposing a major portion of the phosgene in the vaporstream comprising BCl₃, inert gas, and phosgene by heating to a firsttemperature to form a first intermediate vapor stream comprising BCl₃,inert gas, carbon monoxide, chlorine, HCl and less than 10 ppm phosgene;c) adsorbing a major portion of the chlorine in the first intermediatevapor stream at a temperature lower than the first temperature using asolid adsorbent material, thereby producing a BCl₃/inert gas vaporstream comprising less than about 10 ppm phosgene and some HCl; d)routing said BCl₃/inert gas vapor stream comprising less than about 10ppm phosgene and some HCl to a condenser; e) condensing at least aportion of BCl₃ in the BCl₃/inert gas vapor stream in said condenser, toform a first condensed phase comprising BCl₃, HCl and inert gas and asecond vapor stream comprising inert gas, BCl₃, oxygen, and nitrogen; f)routing the second vapor stream to a secondary condenser, thus forming agaseous stream comprising less than about 10 ppm BCl₃ and a secondcondensed phase comprising BCl₃ and HCl; and g) routing the firstcondensed phase to a stripper wherein inert gas is used to stripmolecules having specific gravity less than BCl₃ from the firstcondensed phase to produce a third condensed phase comprising less than50 ppm HCl, and a stripped vapor phase.
 19. A process for increasing thecondensed phase production of BCl₃ comprising less than about 10 ppmphosgene, less than 10 ppm chlorine, and less than 10 ppm HCl, theprocess comprising the steps of: a) introducing an inert gas into acontainer having condensed BCl₃ therein, said condensed BCl₃ havingtherein a minor portion of phosgene impurity; b) converting a majorportion of the phosgene in the condensed BCl₃ to carbon monoxide andchlorine by increasing temperature to produce a phosgene deficientstream; c) decreasing the temperature of the phosgene deficient streamand contacting it with an adsorbent to remove the chlorine in the streamby adsorption to form a chlorine and phosgene free condensed stream; d)stripping the chlorine and phosgene free stream using helium to formBCl₃ product condensed stream; and e) using inert gas to transfer theBCl₃ product condensed stream to a product receiver.